Often when scree forms naturally, a fall of crumbling stones and soil will collect under the high cliff. Most of the soil will be washed away, and gradually a varied heap of stones, to which storms are continually adding, will form. This sort of heap is generally referred to as scree. Nature is very kind, and rarely do we find such stone heaps entirely bare. They may contain what alpine gardeners value highly, such gems as androsace of various, species, and the rare campanula zoyrii.
To copy a rock garden of this scree type is very simple. I have seen it done on the roof of a town house, where a surprising number of plants were grown in small stone chippings, with no ordinary soil at all. Rock plants do not take very kindly to the dirty air of town districts as a rule but in this roof garden of scree only, quite a good collection managed to thrive very well indeed.
Yet another kind of rock garden is the moraine. This is formed in nature by glacial streams. As the ice of the glacier proceed, gradually down the mountain side, it carries with it rocks of various, sizes, and most of these are crushed and pounded to small stones by the time they reach the valley where the ice melts. In this way a stony bed to the melting stream of ice is gradually formed; through the greater part of the year this bed is dry at the surface, while ice-cold water runs through the under layer of stones. Hot sunshine frequently pours down on the surface of the moraine, but always the under layer, where thepenetrate, is moist and cool.
Plants of certain kinds have become adapted to these particular conditions, and if they are to be brought into the garden, and to thrive there, the natural conditions must, as far as possible, be reproduced. All sorts of ingenious methods have been adopted by rock gardeners in the formation of a moraine garden, and there is still room for much originality in this direction. Moraine plants have been cultivated in shallow tanks, slightly sloping, and fed with water at the higher end. The soil has been a specially preparedof sandy, fibrous loam, mixed with crushed charcoal or sphagnum moss and peat, and surfaced with fine, stone chips.
Another good moraine garden was made at the lower end of a rocky cascade, the water being allowed to form a bog, which was surfaced in parts with prepared peaty soil and stone chips. This question of finding a home for moraine plants is definitely one in which the ingenuity of the garden maker can find expression.
A natural spring suggests to any garden maker the formation of some water feature. Such natural springs are frequently found in districts where the subsoil is of rock, and any gardener who strikes one can call himself fortunate. It may be that such a spring occurs in a part of the plot which is open and sunny—in a quarried cliff, for instance. A rippling cascade of water tumbling over rocks and splashing on to drifts of musk, or water forget-me-nots, would suggest itself here. But should the spring be discovered in a stretch of woodland, the stream would almost naturally be planted with moisture-loving ferns and other plants suited to shade. Rather different types of rock would be preferable in the two types—small rocks suitably placed would be good in the sunny stream-side, while bold cliffs of austere character would possibly be more suitable for the shady site.
A spring emerging from a wooded hillside might well be formed at the source into a natural wall fountain or dripping well, with ferns, ramondias, and such plants, set in the vertical crevices of the wet rocks.
Almost any unusual site can, in fact, be worked into a rock garden scheme, and it would be impossible to describe in detail the layout for each. As a matter of interest, the garden maker is reminded that the best rock garden firms do not offer any sort of prepared scheme beforehand for the layout of a new rock garden, but ask for their experienced craftsmen to be allowed a free hand, knowing that they will use stone, plants, environment, aspect, etc., to the best advantage if allowed to create as they work.